Refactor: Use generic Define bound kind

This commit consolidates `DefLocal` and `DefGlobal` into a single
`Define` bound kind. This simplifies the AST and makes it more
consistent.

It also introduces `DeclarationKind` to differentiate between variable
and parameter definitions.

src/ast/compiler/specializer.rs

@@ -104,34 +104,21 @@ impl Specializer {
                     node.ty.clone(),
                 )
             }
-            BoundKind::DefLocal {
+            BoundKind::Define {
                 name,
-                slot,
+                addr,
+                kind,
                 value,
                 captured_by,
             } => {
                 let value = Box::new(self.visit_node(*value));
                 (
-                    BoundKind::DefLocal {
-                        name,
-                        slot,
-                        value,
-                        captured_by,
-                    },
-                    node.ty.clone(),
-                )
-            }
-            BoundKind::DefGlobal {
-                name,
-                global_index,
-                value,
-            } => {
-                let value = Box::new(self.visit_node(*value));
-                (
-                    BoundKind::DefGlobal {
-                        name,
-                        global_index,
+                    BoundKind::Define {
+                        name: name.clone(),
+                        addr,
+                        kind,
                         value,
+                        captured_by: captured_by.clone(),
                     },
                     node.ty.clone(),
                 )